Whats the difference between DX 9a and b.......I've got 9a and was just wondering if I should be using 9b since FS04 came out.

There's a security hole in 9a--now that it has been published, you can bet people are trying to exploit it. 9b also corrects some other issues. Some noted an improvement after loading 9b, but I didn't--having said that both FS2002 and FS2004 were already running on par with the best reports vs. my type of system...